1. Field of the Invention
This invention relates generally to a sealed type fluid reservoir and more particularly to a sealed type fluid reservoir of a brake master cylinder for use in a vehicle brake system.
2. Description of Prior Art
It has been known to use a sealed type fluid reservoir for a brake master cylinder in order to prevent the entrance of air, water or dirt into the brake system from the reservoir.
It has also been known to use a seal member, such as a bellows, diaphragm etc., for sealing the reservoir chamber from the surrounding atmospheric environment. Such seal members are vertically movable within the reservoir chamber in response to variations in the liquid level in the reservoir chamber so as to always maintain the pressure in the chamber at substantially atmospheric level. The range of vertical movement of the seal member is, however, limited by constructive reasons, such as size or space limitation of the reservoir.
One improvement has been made in, for example, U.S. Pat. No. 3,423,939 patented on Jan. 28, 1969, wherein a pressure relief valve is provided for the purpose of relieving any pressure in excess of approximately 1 p.s.i. in the reservoir. According to this prior art, the relief of excess pressure may be possible, but it may be impossible to supply pressure to the sealed chamber when the chamber is subjected to vacuum.